It is oftentimes desirable to inspect a workpiece in order to detect anomalies, such as the effects of corrosion. For example, vehicles, such as aircraft, trains, automobiles and other motor vehicles, and other structures may include a number of structural components that are desirably inspected in order to identify anomalies, such as the effects of corrosion. Although some of the structural components are readily accessible so as to be inspected visually, a number of the structural components, such as the stringers of an aircraft, are positioned in a remote location so as to be hidden from view or to otherwise be of limited access.
For some hidden structures, structural components that are visible and near a hidden structure may be evaluated. An estimate of the condition of the hidden structure may then be derived based upon the condition of the visible structural components near the hidden structure. For example, a beavertail fitting may be attached to a wing skin. A beavertail fitting may be relatively large, such as 17 feet in length for a KC-135 aircraft, and may therefore hide a substantial portion of the wing skin that underlies the beavertail fitting. By evaluating the condition of the wing skin that surrounds and is proximate to the beavertail fitting, such as to identify corrosion, discoloration or pitting, the condition of the portion of the wing skin that underlies and is hidden by the beavertail fitting may be estimated. In an instance in which the wing skin that surrounds and is proximate to the beavertail fitting shows evidence of corrosion, the beavertail fitting may be removed in order to visually inspect the portion of the wing skin underlying the beavertail fitting. The removal and subsequent reattachment of the beavertail fitting following visual inspection of the portion of the wing skin that underlies the beavertail fitting increase the time that the aircraft is out of service and, as a result, may be inefficient in an instance in which the estimate of the condition of the portion of the wing skin that underlies the beavertail fitting is subsequently proven to be incorrect by the visual inspection of the portion of the wing skin that underlies the beavertail fitting.
In order to inspect these hidden structural components as opposed to relying upon an estimate of their condition, a structural assembly may be disassembled and, following inspection, may then be reassembled, thereby resulting in substantial expense and downtime. With respect to an aircraft, for example, the disassembly, inspection and subsequent reassembly may require a number of man hours and lead to significant aircraft downtime at a repair depot. In order to avoid disassembly of a structural assembly, non-destructive inspection techniques have been developed, such as radiography, ultrasonic and eddy current inspection techniques. The type of non-destructive inspection technology that is utilized may be dependent upon the type of anomaly to be detected, the type of material to be inspected, the location at which the inspection will occur and the complexity of the structural assembly in and around the location that will be inspected. For example, the substantial number of fasteners utilized to attach a beavertail fitting to the wing surface may prevent ultrasonic and eddy current inspection techniques from being utilized to inspect the hidden portion of the wing skin that underlies the beavertail fitting, thereby suggesting that a radiographic inspection technique be utilized.
Some remote locations of a structural assembly may be prone to corrosion as a result of the intrusion and retention of moisture. Since the need for corrective action, if any, is dependent upon the severity of the corrosion which may, in turn, be measured by the percent of the total thickness of the structure that has been lost due to corrosive activity, radiography may provide a non-destructive inspection technique to facilitate the inspection of such remote locations without disassembly in order to determine the effects of corrosion. In order to non-destructively inspect a structural component using transmission radiography, an x-ray source may be placed on one side of the structural component and an imaging medium may be placed on the other side of the structural component. As such, while the structural assembly need not necessarily be disassembled during transmission radiography, access is generally required to both sides, that is, the opposite sides of the structural component to be inspected. While access to the opposite sides of a structural component to be inspected is available in some instances, the opposite sides of some structural components may not be readily accessed and, as such conventional transmission radiographic techniques may be unavailable for non-destructive inspection purposes. Moreover, some structural components may be hidden by an overlying structure that has a thickness that is varied, thereby further complicating the radiographic inspection of the hidden structure since the results will also be dependent upon the thickness of the overlying structure through which the hidden structure was inspected. As such, many structural assemblies must be disassembled in order to inspect the structural components that are otherwise hidden from view, thereby materially increasing the time and the labor required for the inspection.